1. Field of the Invention
The invention relates to a method and an apparatus for transferring a web made of a flexible material, especially a paper web, from a web guide surface that outputs the web to a web conveying apparatus.
2. Description of the Related Art
Normally, web transfer concerns the transfer of a threading tail, which is part (for example, an edge strip) of the aforementioned paper web. The transfer takes place, for example, from a first machine section to a following second machine section. Such machine sections can be, in particular, parts of a machine for producing or converting a paper web. For example, it concerns the transfer of the tail within or at the end of the press section of a paper making machine; within or to a winder; and/or from the end region of the drying section of the paper making machine to a following calender. This “tail transfer” is used to make threading the paper web into the machine easier.
It is the intention of the present invention to improve the methods and apparatuses which are described in U.S. Pat. Nos. 3,355,349 and 4,501,643, and also in the brochure “Double Tail Elimination” from the FIBRON Machine Corporation, New Westminster B.C., Canada. Reference is also made to German patent application DE 199 62 731.2.
U.S. Pat. No. 3,355,349 describes a vacuum belt conveyor for conveying a threading strip or tail of a paper web from the drying section of a paper making machine to the first nip of the calender thereof. The belt conveyor includes an elongated body and an air-permeable endless belt, which is mounted such that it can be moved on the body with the aid of two rollers. The endless belt has a conveying run (for example, its upper run). The conveying run travels from the region of the last drying cylinder to the region of the first nip of the calender. The belt is arranged in such a way that it picks up the threading strip from the last drying cylinder. The elongated body of the conveyor is designed as a vacuum box having a perforated upper part. The length of the vacuum box extends underneath the conveying run of the belt. Measures are provided to produce a vacuum in the box, in order to hold the threading strip on the moving belt.
At the infeed end of the known belt conveyor, a severing device or tail cutter is fixed. The severing device or tail cutter is a toothed knife which extends in the transverse direction, i.e., parallel to the roller axis. Before the belt conveyor begins to transport the tail of a web, the complete web, including the tail, runs downward from the last drying cylinder “outputting the web”, past the inlet region of the belt conveyor, the web finally reaching a broke container or a broke pulper. A narrow “tail doctor” is provided on the last drying cylinder, in order to separate the tail from the outer of the drying cylinder and to transfer the tail to the belt conveyor. When the latter comes into action, the tail cutter severs the tail and, in this way, forms a new start of the tail, which is then transported to the calender. If no tail cutter were to be present, the belt conveyor would pull a piece of the tail upwards again out of the broke container and therefore transport a “double tail”. Transporting a “double tail” would cause problems during the threading operation (as addressed in the abovementioned brochure “Double Tail Elimination”).
The belt conveyor design which is disclosed by US '349 and by the referenced brochure has been tried and tested in operation. However, improvements are desirable with the aim that the belt conveyor be able to operate still more reliably and/or at an even higher working speed. In addition, a tail doctor should be avoided, since such an element causes impermissible wear of the outer surface of the drying cylinder.
According to US '643, an apparatus for the transverse severing and guidance of a tail is designed in such a way that it avoids moving parts and a cutting blade or knife. The tail is separated from the last drying cylinder with the aid of two edge blowing nozzles and is severed transversely with the aid of two pneumatic guide plates, which pull the tail in two different directions. The onward transport of the tail is then carried out exclusively by one of the pneumatic guide plates. It is doubtful whether this known design operates satisfactorily, at least when a paper web is to be transferred at a relatively high speed and/or when a very high operating speed is to be used.